Enhancing the electrochemical performance of lignin based supercapacitors via covalent modification of lignin side chains

Covalent modification of lignin side-chain notable enhances its thermodynamic properties. • ALC-4 features a denser structure and a higher graphitization degree compared to counterparts. • Achieves a significant reduction in Rs, accompanied by superior electrochemical performance. • This work expands the application potential of lignin-derived carbon materials in electrodes. Lignin, a low-cost, renewable biomass with high carbon content, shows great promise for electrode materials, yet its side chains tend to cleave and volatilize during thermal treatment, causing structural defects that reduce the graphitization degree of derived carbon and limit electrochemical performance. Herein, isophorone diisocyanate (IPDI) is used as a covalent modifier to cross-link lignin side chains via a polyurethane reaction; subsequent carbonization and activation yield lignin-based carbon materials with high graphitization and superior electrochemical properties. Multiscale characterizations confirm IPDI effectively introduces polyurethane groups, increases molecular weight, and enhances thermal stability by cross-linking lignin side chains. The modified lignin-derived carbon (ALC-4) exhibits a denser surface, more developed graphitic domains, and higher graphitization degree than the unmodified counterpart (ALC-1). Electrochemical tests show ALC-4 has ∼1.6 times lower equivalent series resistance and ∼6.5 times higher specific capacitance than ALC-1. The ALC-4//ALC-4 symmetric supercapacitors delivers 137.74 mF cm −2 specific capacitance, 19.13 mWh cm −2 energy density at 50 mW cm −2 power density, and retains over 90% capacitance after 10000 cycles, providing a promising strategy for high-performance lignin-based electrodes. Download: Download high-res image (250KB) Download: Download full-size image